SEM, EDS and XPS analysis of nanostructured coating formed on NiTi biomaterial alloy by plasma electrolytic oxidation (PEO)

Abstract

Plasma Electrolytic Oxidation (PEO) of NiTi alloy was studied in the electrolyte consisting generally of concentrated orthophosphoric acid with an addition of copper II nitrate. The PEO process was used to obtain a nanostructured coating on the Nitinol surface. The surface layer analyses methods, such as scanning electron microscopy (SEM) with the energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS), allowed determining the structure and composition of the most expected coatings and revealing the conditions for obtaining them. It was found that the porous PEO coating obtained in the electrolyte containing copper nitrate in an amount higher than 1,6 mol/L consists mainly of copper-titanium-nickel phosphates. Moreover, in comparison with matrix, the emergence of carcinogenic nickel appearing in the coating fortunately appears in very small quantities, i.e. below 1 at%.